Glucocorticoids counteract hypertrophic effects of myostatin inhibition in dystrophic muscle
David W. Hammers, Cora C. Hart, Andreas Patsalos, Michael K. Matheny, Lillian A. Wright, Laszlo Nagy, H. Lee Sweeney
David W. Hammers, Cora C. Hart, Andreas Patsalos, Michael K. Matheny, Lillian A. Wright, Laszlo Nagy, H. Lee Sweeney
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Research Article Muscle biology Therapeutics

Glucocorticoids counteract hypertrophic effects of myostatin inhibition in dystrophic muscle

Abstract

Duchenne muscular dystrophy (DMD) is a devastating genetic muscle disease resulting in progressive muscle degeneration and wasting. Glucocorticoids, specifically prednisone/prednisolone and deflazacort, are commonly used by DMD patients. Emerging DMD therapeutics include those targeting the muscle-wasting factor, myostatin (Mstn). The aim of this study was to investigate how chronic glucocorticoid treatment impacts the efficacy of Mstn inhibition in the D2.mdx mouse model of DMD. We report that chronic treatment of dystrophic mice with prednisolone (Pred) causes significant muscle wasting, entailing both activation of the ubiquitin-proteasome degradation pathway and inhibition of muscle protein synthesis. Combining Pred with Mstn inhibition, using a modified Mstn propeptide (dnMstn), completely abrogates the muscle hypertrophic effects of Mstn inhibition independently of Mstn expression or SMAD3 activation. Transcriptomic analysis identified that combining Pred with dnMstn treatment affects gene expression profiles associated with inflammation, metabolism, and fibrosis. Additionally, we demonstrate that Pred-induced muscle atrophy is not prevented by Mstn ablation. Therefore, glucocorticoids interfere with potential muscle mass benefits associated with targeting Mstn, and the ramifications of glucocorticoid use should be a consideration during clinical trial design for DMD therapeutics. These results have significant implications for past and future Mstn inhibition trials in DMD.

Authors

David W. Hammers, Cora C. Hart, Andreas Patsalos, Michael K. Matheny, Lillian A. Wright, Laszlo Nagy, H. Lee Sweeney

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Figure 3

Chronic prednisolone treatment affects skeletal muscle protein balance in vivo.

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Chronic prednisolone treatment affects skeletal muscle protein balance i...
Adult male DBA/2J mice received daily oral treatments with vehicle or 5 mg/kg prednisolone (Pred) for 10 days. (A) To assess relative protein degradation, vehicle- and Pred-treated mice (n = 5–6) received a s.c. injection of 20 mg/kg of the proteasome inhibitor, MG-132, 24 hours prior to terminal endpoint. The accumulation of poly-ubiquitinated (K-48 linkage) proteins was assessed by immunoblotting of quadriceps muscle lysates. (B) To assess relative protein synthesis, vehicle- and Pred-treated mice (n = 6) received an i.p. injection of 20 mg/kg puromycin 30 minutes prior to terminal endpoint. The prevalence of puromycin-labeled peptides was assayed by immunoblotting using an anti-puromycin antibody. Ponceau red staining was used to visualize protein loading for immunoblot signal normalization. (C) Relative gene expression of the ubiquitin E3-ligase, Trim63, in quadriceps muscle of DBA/2J mice following a single dose of vehicle or Pred (n = 3), normalized to Gapdh. Data were analyzed using Welch’s t test (α = 0.05), with effect size reported as Cohen’s d (d). Data are presented as box-and-whisker plots, with minimum and maximum values indicated by error bars; data are shown as mean ± SEM.